Mechanisms associated with a member movable between a position at which the member closes an opening to a confined space and a position at which the member is removed from the opening are known. Mechanisms of this type are used with doors and may be generally characterized as a door check device. Representative prior art disclosures are found in U.S. Pat. Nos. 3,020,581 (Falk), 3,249,961 (Quinn), 3,979,790 (Chiarappa), 4,380,847 (Tajima) and 4,382,311 (Watts). While the prior art is somewhat relevant to the invention, it goes no further than to disclose various forms of door check device, none of which have a capability of being automatically charged thereby to provide a balancing action in assist in movement of a movable member.
Mechanisms in common use for assisting in the opening of doors and lifting of appliance panels, known as "air springs", exert only a pushing force and cannot be recharged when the initial charge is lost through leakage to the atmosphere. Thus, the commonly used air springs must be discarded and replaced, and cannot be used when a pulling force is required.
The prior art also includes U.S. Pat. No. 4,372,461 (Lerman et al) which is also relevant to the invention. To this end, the Lerman et al patent discloses a mechanism connected to a pivotal member, more particularly the cover of a vessel which may be of large size and weight, to assist in movement of the cover between a position at which the cover closes an opening to a confined space and a position removed therefrom. According to the Lerman et al patent, in addition to providing a capability of assist in movement of the cover, the mechanism also will permit the cover to move to and remain in substantially any position between its limits of movement without support. In addition, the mechanism will prevent movement of the cover in an unimpeded manner to the closed position.